Catfish farming is the largest segment of aquaculture in the US. Catfish are primarily cultured in watershed ponds and are harvested by seining. Despite land and labor costs, pond production can be profitable if water quality is prudently managed. When pond dissolved oxygen (DO) concentrations are low (<2-3 mg/L), the ponds must be aerated to ensure the health of the fish. Aeration is the principal management tool that allows growers to achieve higher feeding rates, increased production, and decreased cost per unit fish produced. US Department of Agriculture research shows that feed conversion ratio (FCR) can be significantly improved by raising the DO concentration above 3.0 mg/L (although catfish can survive at substantially lower levels). At elevated DO levels, the aquaculture process is generally more efficient because the catfish grow faster in a shorter production period, and also have better survival rates.
The catfish aquaculture industry currently relies primarily on rotary “agitating-type” surface splash aerators to aerate aquaculture ponds. Agitating-type aerators are generally powered with 10-hp (7.5-kW) electric motors and average industry usage is approximately 2.6 hp (1.9-kW) per acre.
Paddle-wheel aerators are a common example of agitating-type aerators. While paddle-wheel aerators add significant amounts of oxygen to the water, they are required to mechanically move large amounts of water to be effective. While this is acceptable for routine operations, when the DO level drops to very low concentrations (as when a plankton bloom dies and decomposes), a paddle-wheel aerator will frequently not immediately produce a DO concentration high enough to keep affected fish alive. If a large number of portable (tractor-powered) aerators are not immediately brought in to assist with the emergency aeration, the affected fish will be severely stressed and may die.
The prior art also includes aeration systems with a concentric pipe design. Concentric pipe aerators draw water into an annulus between a relatively large outer casing and a smaller diameter inner pipe. Compressed air is directed into the inner pipe so that pond water circulates down annulus and then up through the inner pipe and back into the pond. However, this design has proven impractical because of the relatively large size requirements for the outer casing and because the annulus is prone to plugging by mud and pond debris. Systems with a concentric pipe design can also be relatively difficult to clean and repair.
The need exists for a system and method for aerating aquaculture ponds that efficiently maintains a healthy aquaculture environment and is capable responding quickly to temporary conditions that cause low oxygen environments. The current invention comprises a method and apparatus that relies on an injection of pressurized air to create a hydrostatic imbalance (rather than a mechanical agitator) to circulate aquaculture pond water and thereby aerate the aquaculture pond.